1. Field of the Invention
The present invention relates to Microwave/mm-wave band MMIC oscillator. More specifically, the present invention relates to the method to a high RF power and differential RTD-HBT oscillator which is a key element for wireless communication systems.
2. Description of the Related Art
Recently, the demand of the microwave and millimeter-wave wireless communication systems including the application areas of satellite communication, wireless LAN and local multipoint distribution services (LMDS) has been greatly increased. In these systems, a voltage controlled oscillator (VCO) is a crucial circuit block, which is used as a local oscillator or up and down converters. For the VCOs, one of the important performance requirements is low power consumption.
In order to achieve the microwave signal generation at low power, the development of the negative cell, which operates at low bias voltage and current, is essential. The conventional negative resistance cell for microwave and millimeter-wave VCOs is comprised of the conventional 3-terminal devices, such as heterojunction bipolar transistors (HBTS) or high electron mobility transistors (HEMTs), or the conventional 2-terminal devices, such as the Gunn or IMPATT diode. However, the negative resistance cell based on the conventional devices usually requires high bias voltage and high bias current for operating at microwave and millimeter-wave ranges. Therefore, as an alternative approach, a tunneling diode (TD), which is one of the most matured quantum devices, has attracted a great deal of interests for the low-power microwave and millimeter-wave VCO due to the high current density and the unique 10 negative differential resistance (NDR) characteristics which arise at a low applied voltage range from the quantum transport phenomena at room temperature. FIG. 1 shows an DC I-V curve of the tunneling diode, As shown in the FIG. 1, the negative differential resistance is generated at the forward applied bias voltage. In particular, the InP based resonant tunneling diode (RTD) shows a negative differential resistance in the low applied bias voltage about below 0.5 V, and shows an high cutoff frequency. In previous works, several tunneling diode oscillators have been demonstrated especially for their advantages of high-frequency and low power consumption. (Ref: (1) V. P. Kesan, A. Mortazawi, D. R. Miller, V. K. Reddy, D. P. Neikirk, and T. Itoh, “Microwave and millimeter-wave QWITT diode oscillators,” IEEE Trans. Microwave Theory Tech., vol. 37, no. 12, pp. 1933-1941, Dec. 1989. (2) M. Reddy, R. Y. Yu, H. Kroemer, M. J. W. Rodwell, S. C. Martin, R. E. Muller, and R. P. Smith, “Bias stabilization for resonant tunnel diode oscillators,” IEEE Microwave Wireless Comp. Lett., vol. 5, no. 7, pp. 219-221, July, 1995.)
Moreover, in order to improve the performance of the oscillators, the MMIC oscillators which are implemented on the stacked-layer structure, have been reported, where the varactor, the 3-terminal devices and the tunneling diode are monolithically integrated. (Ref (3) A. Cidronali, G. Collodi, M. Camprini, V. Nair, G. Manes, J. Lewis, and H. Goronkin, “Ultralow DC power VCO based in InP-HEMT and heterojunction interband tunnel diode for wireless applications,” IEEE Trans. Microwave Theory Tech., vol. 50, no. 12, pp. 2938-2946, Dec. 2002. (4) S. Choi, B. Lee, T. Kim, and K. Yang, “5-GHz VCO with a wide tuning range using an InP-based RTDIHBT technology,” the 12th European Gallium Arsenide and Other Compound Semiconductors Application Symp., Amsterdam, Netherlands, Oct. 11-12, 2004, pp. 207-210)
The stacked-layer heterostructure design implementing the VCO provides the following advantages. First, by integrating the varactor which has a large capacitance ratio, the VCO with a wide tuning range can be easily implemented. Second, the transistor-amplifier output buffer for isolating the output load from the VCO core can be monolithically integrated with the VCO core to prevent the loss of the RF power. Third, the conventional 3-terminal based ICs, such as HBT ICs or HEMT ICs, can be monolithically integrated with the tunneling diode VCOs. Hence, the wireless communication systems, which are composed of VCOs, flip-flops, and amplifiers, can be also monolithically implemented based on the TD-based IC technologies. However, the developed TD based VCOs have several problems; First, they can not generate the differential sine wave signal which is essential for circuit block in the wireless communication system such as a frequency synthesizer. Second, the RF power generating from the TD based VCO is small for the wireless communication system. The narrow Negative Differential Resistance Region of the Tunnel Diode reduces the RF power.